Gas lasers are excited by plasma that is generated in so-called discharge chambers. The plasma can be generated by RF energy, e.g., at 13 MHz or 27 MHz.
At present, the overall RF power that is required for operating a CO2 laser is generated by a single RF power generator and guided into the discharge chamber, where it is divided onto individual discharge paths. Such a system is described, e.g., in U.S. Pat. No. 6,539,045. Uniform distribution of the RF power is very complex and depends substantially on the mechanical and geometrical conditions of the discharge chamber and the discharge paths. Variable excitation of individual discharge paths can be possible using complex switches.
CO2 lasers are often operated in a pulsed manner at frequencies between 10 Hz and 200 KHz. A gas laser is switched on and off at very short intervals if it is used, e.g., for cutting sheet metal. The plasma for generating the laser is re-ignited during pulsing and also for each turn-on or ignition. During ignition very high voltages are used and the plasma load has a very high impedance. Both factors can cause the RF power generator to be heavily loaded. The impedance drops very quickly to very low values after ignition, that is, during full power, and the load is adjusted for operation during full power. For this reason, the major part of the power is reflected by the plasma load during ignition.
In order to facilitate ignition, an ignition aid is frequently provided in the discharge chambers, as is disclosed in U.S. Pat. No. 5,434,881, which provides an excess field substantially due to its mechanical structure, thereby producing locally limited plasma discharge even at low powers. This locally limited plasma discharge produces a sufficient amount of electrons and ions, such that the plasma quickly spreads in the whole discharge chamber when additional power is supplied.
However, these ignition aids produce undesired inhomogeneities during operation at full power, and these inhomogeneities can produce sparkovers at high powers.
In some ignition aids, an additional generator applies a particularly high voltage to a separate electrode pair at the time of ignition. Such ignition aids can be more expensive and can include additional components.